The 80s band Van Halen famously (or infamously) had a rider in its contract which required promoters to provide the band a large number of M&Ms in the dressing room. But brown M&Ms were forbidden. If the band found a single brown M&M, the promoter forfeited his earnings. Why? David Lee Roth explains in this video.

It was actually a clever test. Van Halen stage shows were elaborate productions. To get ready, a promoter had follow a set of lengthy, complex instructions provided in the contract. The brown M&M provision was buried, at random, among these instructions. If the band members went backstage and found brown M&Ms, that meant that the promoter had not read the instructions and there were potential problems with the show.